|Topic Review (Newest First)|
|04-16-2019 09:28 AM|
|alfaparticle||Jim first advised me to advance the intake to below 100 was when I first met him at Watkins glen in 2015. The very fast 1500 Giulietta that he was supporting was running about 98/108 and he thought that my motor would benefit from similar timing. I was unable to advance the 575 that much with the Venolia pistons but road testing indicated that 101 was better than 104. My sessions on Al's dyno showed that 101 was better than 104 and 98 was best of all. The dyno charts show that the improvement was from 3000 rpm to 6200 and they were the same above 6200.|
|04-16-2019 07:25 AM|
I have never used "EFFECTIVE CAM CENTERS" that far advanced as it "would & should" bias the power band to lower RPM ranges (Which you might want for a street car)
Given: Jim`s head mods and intake designs and piston shapes are VERY different.
Most racers using my "race cams" typically find good results using my base line LCs of 104/104 or 104/106. Both of the engines in my two race cars are set at 103/106 now. A 104-105 LSA seems appropriate for the typical Alfa intake length. BUT, I`m using a shorter intake track length with very large raised ports (short custom manifold, 1" air horns in the cold air box) and 50mm DCO carbs. Hayes Flynn`s 230hp/215 hp (different RjR cams in same engine) and Ed`s use only a modified factory airbox (rounded 52mm openings to the 45 DCOE carbs I modified internally).
All these intake track differences have to be considered when choosing LCs of any cam, and the dyno adjustments are pretty much required to optimize the power band.
Key points of making real power are closing the intake valve "early" enough to limit the amount of reversion, and delaying the opening of the exhaust (and still get it closed before P to V issues) to lengthen the power stroke.
My newest Race intakes have total "off the seat duration (at .010" "lash" settings of 298* int. and 276* exh. Key points are durations at .050 are 265* int and 246* exhaust which is where "flow" really starts, and very high durations from there upward 125* int and 110* exh at 450 lift. (Total lifts are .525 int. and .495 exh)
|04-15-2019 08:27 PM|
|Curtis||Interesting Ed, The 2L must be more different than my 1600 than I thought. The dyno has never suggested I advance a 1300 or 1600 intake past 102 and they usually seem happiest around 104. This includes my current engine with Steve's intake and RJs exhaust. If I ever build a 2000 I better ask around I guess!!|
|04-15-2019 07:22 PM|
Jim Steck's motors are typically 98/108. Msiert's black spider road car made 167 HP at the wheels on pump gas. Steve Schwitters built the motor and it was about 98/108. My street motor made 155 HP at the wheels with RJ575/457 cams at 98/108.
|04-15-2019 06:33 PM|
|Curtis||Great to know. Thanks for posting. AlfaParticle who are the big power guys running 98-99 degree intake lobe center and what cams are they doing it with? At least in a near full or full race application it's hard for me to imagine advancing the intake that far not having a detrimental effect.|
|04-15-2019 05:28 PM|
Originally Posted by 930cabman View Post
Even a blind squirrel finds a nut sometimes.
|04-15-2019 05:13 PM|
Dumb luck is better than no luck.
Thank you for sharing
|04-14-2019 02:12 PM|
Originally Posted by alfaparticle View Post
I'll take the timing changes to heart though after that.
|04-14-2019 12:48 PM|
I posted my comments because our cam choice was an expedient, the result of me deciding that I didn't want to take the time to notch the cam follower bores so I could run my 12mm Delta cam. The results were so surprisingly good---much better than I was expecting---that I thought I would add a factoid on cam choice to the BB's knowledge base. Using asymmetrical cams remains something of a black art and so I think it's fun to accidentally stumble across something that works. Is this the best combination? Nope. And I don't think it makes the hp of the Delta A474 12mm cam/Centerline 11.1mm combination which will go on the new head I intend to build. That said, I posted my comments because the combination works real good. If you have a stock Spica cam to use, the Centerline 11.1mm cam sells for $229US. That's a cheap entry fee for the kind of performance improvement you'll get.
|04-14-2019 10:32 AM|
|alfaparticle||Slowcreek, I think that you could pick up maybe 5 HP with a change of LC's. I would advance the intake one hole to about 99 and verify that you have at least .050" piston-valve clearance then retard the exhaust two holes to about 108 and check that you have at least .100" clearance. Then take it back to the dyno.|
|04-14-2019 08:59 AM|
Originally Posted by alfaparticle View Post
|04-14-2019 08:21 AM|
|04-14-2019 07:49 AM|
|slowcreek||So me and 180OUT dodged a bullet?|
|04-14-2019 06:42 AM|
The exhaust cams in all the Spica, Weber and FI engines are the same lobe design as the intake in those motors. The exhaust cams in them are not good designs for that purpose.
In engines built for the Motronic FI system with the large diameter BC intake that exhaust cam is a much better exhaust lobe design and the one I suggest using with the likes of the 10548 cam, and mild aftermarket cams on the intake.
|04-14-2019 01:00 AM|
Originally Posted by 180OUT View Post
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